Purpose of the Experiment
Titration is an analytical technique that is used to determine the concentrations of the substance being sought by gradually adding a titrant of precisely known chemical composition and concentration to the solution under study. This procedure is also performed in this reaction, where a sodium hydroxide solution with the specified characteristics (C = 0.1 M, V = 13.61 mL) was used as the titrant and potassium hydrogen phthalate was used as the test solution; three tests in total were performed in order to minimize calculation errors. The data were taken from a video of the experiment conducted by Dr. Mauser on his YouTube channel (Biochemistry with Dr. Mauser, 2018). Thus, the overall goal of the present experiment was to use potassium hydrogen phthalate to standardize sodium hydroxide, that is, to verify the real alkaline concentration during titration.
Balanced Chemical Reaction
In this process, sodium hydroxide was added dropwise to potassium hydrogen phthalate as shown in the reaction below. A measure of their interaction was the use of the phenolphthalein indicator, which reflected the equilibrium point at which sufficient NaOH was formed in solution and no longer reacted. Thus, the process produced sodium potassium phthalate and water as shown below:
- NaOH + C6H4(COOK)(COOH) → C6H4(COOK)(COONa) + H2O
Or in abbreviated form:
- NaOH + KHP → NaKP + H2O
Stoichiometrically, this equation shows that all reagents and products related to each other as one to one, indicating equality of their molar ratios.
Calculations
The ultimate goal of this experiment was to determine the average concentration of sodium hydroxide, and the calculations were done through potassium hydrogen phthalate, which is stoichiometrically bound to alkali. Therefore, to begin with, the number of moles for potassium hydrogen phthalate in each of the three tests were found based on the masses calculated on analytical weights:
The moles for the sodium hydroxide that was used as the titrant for each of the three tests could also be calculated. In fact, the calculation of the moles had to be done stoichiometrically by the coefficients in the above reaction, since this determined the actual amount of sodium hydroxide that was used. Since potassium hydrogen phthalate was correlated by coefficients with alkali as one to one, this means that the number of moles of sodium hydroxide in each of the tests was equal to the moles of potassium hydrogen phthalate, that is:
It was now possible to calculate the molar concentration of sodium hydroxide after each test. To do this, it was necessary to remember that the volumes of alkali were measured in milliliters, so for correct calculations they had to be converted to liters, namely:
Average Concentration of NaOH
Then the average concentration of sodium hydroxide after all three tests was:
Percent Error
Given that the stated concentration of NaOH was 0.1 M and the actual concentration was 0.1053, the percentage error could be calculated:
That is, the percentage error was much less than 1%, indicating extremely high reliability of the calculations in this experiment.
Reference
Biochemistry with Dr. Mauser. (2018). CHEM 408 — standardizing titrant with KHP [Video]. YouTube.